The zoom function with the mouse wheel sometimes zooms uncontrollably
I recently had this same problem in Blender 2.72 with no apparent answer. However, I found that by pressing Shift - C re-centered the Viewport and then I switched from User Perspective to User Ortho with NumPad 5, and everything returned to normal. I too experienced uncontrollable zooming that led to unquantifiable Location coordinates, but this method worked for me, I hope it solves your problem.